In power presses, often the press is stopped after each operating stroke by the application of friction brakes acting upon the drive system of the press. These brakes are applied when the press reaches a certain position in its cycle and a stop signal is created. At the time the brakes are applied, the main power to the drive system is disconnected. In this manner, the brake stops the power press at the end of each cycle. In some power press operations, multiple cycles are performed before a stop signal actuates the brake and disconnects the power to the press drive system.
When the brake of a power press becomes worn or defective, it must be repaired or replaced to assure safe operation of the press. Under normal circumstances, deterioration of the power press brake is not recognizable until the brake has developed a substantial defect. For this reason, preventive maintenance is often required which involves the periodic repair and/or replacement of brakes which are still functioning properly. This type program requires a substantial amount of labor and time and adds to the total expense of operating power presses. Thus, there has developed a substantial demand for a device which will indicate when a power press brake should be replaced or repaired. Indeed, federal regulations are now being imposed which require that power presses be monitored in their braking cycle to determine when brakes deteriorate to a certain condition. The monitored condition still allows safe operation but indicates that a repair or replacement is needed. To satisfy the desire to eliminate unnecessary, periodic preventive maintenance on power brakes and also to meet the federal regulations, power press manufacturers and users are now in the process of developing systems for monitoring the operation of a power press brake during each braking cycle. Most of these systems involve the use of a cam which indicates overtravel at the end of a stroke or press cycle. These systems require sensitive mechanical adjustments and can often provide false deterioration signals due to shifting of the cams and their position of operation.